Light emitting elements, such as light emitting diodes (LEDs) and laser diodes, which use a Group III-V or Group II-VI compound semiconductor material, may render various colors such as red, green, blue, and ultraviolet by virtue of development of thin film growth technologies and materials constituting the elements. It may also be possible to produce white light at high efficiency using fluorescent materials or through color mixing. Further, the light emitting elements have advantages, such as low power consumption, semi-permanent lifespan, fast response time, safety, and environmental friendliness as compared to conventional light sources, such as fluorescent lamps and incandescent lamps.
Therefore, these light emitting elements are increasingly applied to transmission modules of optical communication units, light emitting diode backlights as a replacement for cold cathode fluorescent lamps (CCFLs) constituting backlights of liquid crystal display (LCD) devices, and lighting apparatuses using white light emitting diodes as a replacement for fluorescent lamps or incandescent lamps, headlights for vehicles and traffic lights.
FIG. 1 is a view briefly showing an energy band diagram of an active layer in a general light emitting element.
Generally, the active layer has a multi-quantum well (MQW) structure including quantum barrier layers and quantum well layers, which are alternately laminated. Stress may be generated in the active layer due to a lattice constant difference between materials constituting the quantum barrier layers and quantum well layers and, as such, polarization may occur in the active layer. As a result, energy band of the active layer may be bent.
When polarization occurs in the active layer, distribution of electrons is inclined toward a p-GaN layer, whereas distribution of holes is inclined toward an n-GaN layer, as shown in FIG. 1. As a result, recombination efficiency of electrons and holes is reduced and, as such, light emission efficiency of the light emitting element is reduced.
Therefore, it is necessary to relieve stress of the active layer while enhancing light emission efficiency of the light emitting element.